This invention is concerned with a process for injecting brown coal or lignite into a blast furnace through the tuyere arches or notches. In this specification, the terms brown coal and lignite may be used interchangeably, in other words, a reference to brown coal is intended to include lignite and a reference to lignite is intended to include brown coal; in this connection it may be noted that, although brown coal and lignite are generally considered as the same material, there may possibly on recent knowledge be a difference betweeen the two types of material, both of which are therefore encompassed by the present invention. For convenience and brevity, the term brown coal is generally used in this specification to denote both forms of material.
Many efforts have been made, over a substantial period of time, to reduce the consumption of coke in a blast furnace by using a low-cost fuel and/or by directly introducing reduction agents into the blast furnace. Thus, the introduction of heavy oil has been proposed in this respect. It is also known for reduction gas mixtures which predominantly comprise H.sub.2 and CO and which are possibly produced by regeneration of waste outlet gas to be blown into the blast furnace, either into the hearth thereof or into the lower region of the actual blast furnace stack.
The injection of fine-grain coal, including brown coal or lignite, into the blast furnace, has long been the subject of tests and endeavours in this respect. Although the marked increase in recent years in the price of fuel oil has inevitably encouraged the use of coal wherever coal is available more cheaply than oil, the injection of coal into the blast furnace under practical operating conditions has hitherto been used only to a very limited extent. This is due on the one hand to the fact that the transportation and distribution of fine-grain coal from a supply container into the injection blowing opening of the blast furnace involve greater difficulties than when using a fluid agent, for example oil or gas. Added to this is the fact that normally the necessary conditions for a rapid and therefore complete conversion reaction within the blast furnace are much more favourable when using oil and gas than when using a solid fuel. In this respect, account should be taken of the fact that reaction of the fuel introduced must be as complete as possible, if only for reasons of cost. In addition, incomplete reaction, particularly in the case of solid fuel, would generally result in serious disturbances and even breakdowns in operation of the blast furnace, for example due to the production of soot or black which would reduce the permeability of the blast-furnace burden in regard to the flow of reduction gas and which would possibly also be present in the outlet gas. The latter can result in operational problems in the pieces of equipment through which the outlet gas flows. Although the use of brown coal dust or lignite dust as an additive fuel has already been under discussion for more than ten years, see for example Neue Hutte, 10th edition, issue 12, pages 708 to 710, use thereof in practice has been limited just to test operations. This is evidently because no one has hitherto succeeded in completely and satisfactorily solving the questions and problems concerned with the complete reaction of the brown coal in the hearth of the blast furnace. Thus, in a discussion paper by J Mangelsdorf in `Le coke en siderurgie`, in connection with the Charleroi International Congress, 1966, page 535, it is pointed out that, with the increasing addition of brown coal dust or lignite dust to for example 150 to 160 kg/tonne of crude iron, the exchange relationship of a kilogram of coke per kilogram of brown coal or lignite dust is considerably reduced.
In Erdol, Kohl, Erdgas, Petrochemie, 18, 1965, pages 112 to 118, there is a report about research into and testing of combustion or gasification performances of particular auxiliary fuels in the tuyere arches or notches. The view expressed is that the combustion and gasification of fine coal is more complicated and slower in comparison with natural gas and heating or fuel oil, as a number of steps are involved, some of which are carried out in succession while others are performed in parallel. In this respect it is stated that only grains with a diameter of more than 1 mm are completely degassed in the heating region, whereas smaller grains are first discharged with the flow of gas from the heating region as a result of their lower speed of downward movement.